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Abstract
A population of the virile crayfish, Orconectes virilis (Hagen, 1870), has been recorded within the River Lee system of North
London in the United Kingdom. First detected in 2004 and thought to be the spiny-cheek crayfish, Orconectes limosus (Rafinesque,
1817), a recent re-examination of the specimens has confirmed that this is the first recorded breeding population of O. virilis in the
United Kingdom. A monitoring programme is being established to assess the rate at which the species colonises the catchment and
its ecological impact.
Key words: crayfish, Orconectes virilis, River Lee, London

The virile crayfish, Orconectes virilis (Hagen,
1870), occurs naturally in many regions of the
USA and Canada, but it has also been introduced
to other regions in North America and into
Chihuahua, Mexico (Hamr 2002). It is
considered to be an invasive crayfish and there
are currently concerns that it might displace
native crayfish in eastern New Brunswick,
Canada (McAlpine et al 2007).
In Europe attempts were made to introduce it
into France in 1897 and Sweden in 1960 but
these were unsuccessful (Souty-Grosset et al.
2006). It has subsequently been recorded in the
Netherlands where it is believed to have
originated from the aquarium trade. Here it has
established over recent years and is becoming
more widespread with damage to dykes and
submerged vegetation being a consequence of its
presence (Pöckl et al. 2006). It now appears that
a similar event has taken place in the waterways

102

of the River Lee catchment in North London
where O. virilis is now established (Figure 1).
In 2004, crayfish originally believed to be the
spiny-cheek crayfish, Orconectes limosus
(Rafinesque, 1817), were discovered in a
concrete lined pond in Enfield. These were
locally reported to have occurred as the result of
a local resident disposing of his collection of
exotic aquarium pets prior to moving house. The
watercourses in this area of the catchment form a
complex network which link in and out of the
Lee Navigation. Further populations have now
been recorded in adjacent watercourses within a
7 km radius of the suspected point of
introduction (Figure 2), suggesting a dispersal
rate of more than 2 km a year.
Orconectes virilis has been found in low
numbers at the sites where it has been recorded
and has not displayed the characteristically
aggressive response of the signal crayfish,

Orconectes virilis identified in the UK

Figure 1. A male virile crayfish, Orconectes virilis, collected from the Lee Navigation, North London in 2006 (Photo: DM Holdich).
Note that the left cheliped is of a Form I sexually active individual, whereas the regenerating right cheliped is that of Form II
sexually inactive individual. It should also be noted that the colouring of this specimen, which had been frozen, is not the same as
that of a fresh specimen.

Figure 2. The current distribution of Orconectes virilis in the
River Lee catchment, North London. The right hand map
gives an overview of dispersal. The left hand map shows the
source and its believed relationship to the watercourses where
O. virilis is currently found. (Map: A. Ellis).

Pacifastacus leniusculus (Dana, 1852), when
handled. Initial inspection of the catch returns
from trapping have shown carapace lengths,
measured from the tip of the rostrum to the base
of the carapace, ranging from 29 mm to 79 mm.
The presence of O. virilis is a further threat to
the UK’s indigenous white-clawed crayfish,
Austopotamobius pallipes (Lereboullet, 1858)
(Holdich et al. 2004), as it is a potential vector of
the crayfish plague, Aphanomyces astaci
Schikora (Saprolegniales). As only the second
known country of occurrence within Europe, it
will be interesting to see which habitats this new
resident occupies, if it burrows like O. limosus,
if it continues to spread, and how it will interact
with the already cosmopolitan communities
within this network of watercourses. The
following invasive species, Chinese mitten crab,
Eriocheir sinensis (H. Milne Edwards, 1854),
topmouth gudgeon, Pseudorasbora parva
(Temminck et Schlegel, 1846) and zebra mussel,
Dreissena polymorpha (Pallas, 1771), are
recorded from the same watercourses as
O. virilis. Within the River Lee catchment two
other species of alien crayfish are also present,
P. leniusculus and narrow-clawed crayfish
Astacus leptodactylus (Eschscholtz, 1823).

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D. Ahern et al.

An on-going monitoring programme is being
established to assess the progress of O. virilis
within the River Lee catchment. It is hoped that
the detection of this species in an early stage of
its establishment will lead to an unusual
opportunity to record, as comprehensively as
possible, the potential impacts of O. virilis.
Acknowledgements
Thanks are due to David Holdich for confirming the
identification and for making useful comments on the
manuscript.